I think the worse logic questions are in the PR workbook; my personal opinion.
Nevertheless, if I understand it correctly, the decrease in productivity happns becuase they just took a lunch break and digesting food with their brain
Thus, the productivity falls.
Also, it is not very possible to persuade people to take their lunch break just before they are leaving work unless they come in at 10.
I think I totally missed the point, so you may have to explain it to me again. Your writing seems to be quire resistant for my head, am I getting old?